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Farsi, Alessandro

Abstract

Nonlinear (NL) optics differs from its linear counterpart in that it drives interaction between different optical frequencies. In a stimulated parametric process, such as sum/difference frequency generation in in [chi](3) , [chi](2) media or phase conjugation a strong pump drives the interaction with a weaker signal field, and an idler field is generated at a different frequency set by the energy conservation of the process. In this work we focus on a subset of possible interactions, i.e. fre- quency translations, in which, for a generated idler, the signal undergoes depletion and the total energy of the two fields is conserved in the Manley-Row sense (i.e. number of photons is conserved). While for most applications such distinction is not fundamental, it becomes a crucial aspect in the very-low-power and quantum regimes. The focus of this work is Bragg Scattering (BS) in [chi](3) medium, a parametric four wave mixing interaction where two pumps separated by an angular frequency detuning [INCREMENT][omega] drive the interaction between a signal and an idler separated by the same amount. This configuration offers great flexibility with respect to choice of participating fields, enabling translation across both a wide span of wavelength and small detuning within the same frequency bands. We first utilize BS to demonstrate an unusual phenomena known as temporal cloaking : a coherent optical manipulation that hides events from an observer. Using the concept of space-time duality, we implement a novel split time-lens that opens and closes a gap in a continuous wave (CW) probing signal, in which events can happen undetected. The reversibility of frequency translation enables us to do and undo the gap without adding any noise. Successively, we employ BS in the quantum regime: time-reversibility implies the preservation of quantum coherence so that quantum states can be manipulated without affecting their quantum nature. Frequency translation offers a way to connect elements operating at different wavelengths for a large scale quantum system. We use BS to operate on single photon states: we demonstrate high performance implementation using a nonlinear fiber, achieving efficient translation of 94 % while having low-losses and extremely low noise compared to previous demonstrations. With such system, we are able to implement more complex manipulation of the quantum field performing temporal compression and magnification using a time-lens. Since frequency translation provides us with the ability to coherently couple arbitrary pairs of frequencies, it is natural to introduce the concept of chromatic qubits, a frequency encoding that is naturally controlled by BS. We manipulate such qubits using a sequence of two BS interactions in a Ramsey interferometer configuration: by varying the delay between the two stages, we observe fringes of interference between the two possible output frequency states. Finally we propose an extension of BS to control high-dimensional frequency space, and study theoretically the different regimes of BS interaction in densemultiplexed frequency channels in the presence of multiple pumps.